1. Field of the Invention
The present invention relates to a resin composition to be used as a material for a core portion of an optical waveguide, and to an optical waveguide produced by using the resin composition. More specifically, the present invention relates to a resin composition which permits easy formation of a core pattern in an optical waveguide with the use of an alkali developing liquid, and to an optical waveguide produced by using the resin composition.
2. Description of the Related Art
Optical waveguides are typically incorporated in optical devices such as optical waveguide devices, optical integrated circuits and optical wiring boards to be widely used for optical communications, optical information processing and other general optics. Such an optical waveguide typically includes cores of a predetermined pattern provided as light paths, and an under-cladding layer and an over-cladding layer covering the cores.
Where the cores, the under-cladding layer and the over-cladding layer are formed in predetermined patterns, various materials are generally usable. For example, a photosensitive polymer material is used for forming the cores in the predetermined pattern. The formation of the cores is achieved in the following manner. A coating layer of the photosensitive polymer material is formed on the under-cladding layer, and irradiated with ultraviolet radiation via a patterning film for exposure. Then, an unexposed portion of the coating layer is removed with a solvent. Thus, the coating layer is patterned to form the cores in the predetermined pattern. This core formation method is easy and less expensive, but uses the solvent for the patterning, thereby posing a problem associated with working safety and environmental load.
To cope with this problem, a photo-curable and thermo-curable resin composition containing an alkali soluble resin, an photopolymerization initiator and an epoxy resin has been developed as an alkali developable optical waveguide material, which is used as a core material to form the core pattern by using an alkali developing liquid instead of the solvent (see JP-A-2005-338202).
After the core pattern is formed by using the alkali developable optical waveguide material (photo-curable and thermo-curable resin composition), a carboxyl group (acid functional group) in the alkali soluble resin and an epoxy group in the epoxy resin are esterified through thermosetting for improvement of reliability characteristics such as heat resistance and moisture resistance.
However, the epoxy resin in the photo-curable and thermo-curable resin composition disclosed in JP-A-2005-338202 does not have the carboxyl group (acid functional group) and, therefore, is insoluble in the alkali developing liquid. After the development, the alkali developing liquid is liable to contain insoluble suspended and precipitated substances and, therefore, is poorer in use efficiency, thereby reducing the mass-productivity with a difficulty in the quality control thereof. If the alkali developing liquid containing the insoluble suspended and precipitated substances is continuously used for the development, the suspended substances are liable to adhere again to a surface of the core pattern, making it impossible to properly configure the core pattern.
A resin composition is provided which permits easy formation of the core pattern of the optical waveguide by using the alkali developing liquid and suppresses degradation of the alkali developing liquid for improvement of the productivity, and to provide an optical waveguide produced by using the resin composition.